This caterpillar puts up an impressive display of defences. An bushy density of barbed utricating hairs covering every segment, pointed in all directions. And for all that they mean naught to our elegant little wasp, the wasp with iridescent wings, and a fragile waist. A slick player so small that it gets lost within the defences of the caterpillar. It is precisely because it is so small that it can get past the hair that keep large predators and perhaps even larger wasps away. Good things, small packages.
It is leaving some packages of its own behind. This is a parasitoid wasp. Such an innocuous sounding word, not parasite, merely like a parasite. An -oid, eidos, form of, an imperfect resemblance. But this imperfection is not in the least bit innocuous, it is very very sinister. This wasps imperfection is that it will kill the caterpillar. Well, its progeny will. The eggs it is laying in that caterpillar will hatch into larvae. These larvae will feed on the caterpillar from within until they are ready to pupate. At this point they will eat their way out of the caterpillar, now an emptied and dead cul-de-sac, and will pupate once outside.
A good parasite loves its host. It keeps it alive. In possibly the most ancient case we know, it loves it so much it nurtures it (our lovely endosymbionts: mitochondria, chloroplasts). The perfect parasite is one where the host cannot live without its parasite. To kill your host means you must find another one: a very imperfect situation. So, a parasitoid, an imperfect parasite.
'I'm Gentleman Death in silk and lace, come to put out the candles. The canker in the heart of the rose.'